Hi Ulrich and others,
I picked up a cheap 2nd-hand Lenovo T520 and it works well with the Madiface. I just recorded my school's annual music concert with it (only 8 channel's via a Micstacy, so not sure about larger i/o requirements. I'll try to test this out when I get a chance). What is great is that I could also control the preamp's gain using the RME MidiRemote program, and with the Madi card installed in the Micstacy, I could also send 8 channels back out through the Micstacy's adat ports for the fold-back and PA speakers, each with separate sub-mixes, using TotalMix.
A Madiface setup is an incredibly flexible system when you find a suitable laptop. DPC latency with this particular Lenovo is pretty good (I get one smallish spike every 70 seconds without fail, but it still remains within the green safe region). I did no involved OS tweaking and have not even done a clean OS install, so the Lenovo utilities & bloatware that come with this laptop do not seem to do any harm. I will soon be installing a tiny mSata as my OS boot-drive and will then do a clean OS install, so it will be interesting to see if that makes a difference, however I suspect not much. I have also heard good reports about the Lenovo T420. These Lenovo's both use the newer Intel chipsets and have the necessary express-card slot.
As regards graphics cards, my T520 uses only the on-board Intel HD 3000 graphics, no discrete graphics card. For audio use, I think this is absolutely fine. Discrete graphics cards for simple audio recording are often overkill and a possible source of problems, as the 3rd-party drivers can be the cause of DPC spikes leading to audio glitches. The Lenovo's can be configured with high-res screens, however mine is a lowly 1366x768. As I did not configure it nor buy new I had no choice, but if this is important to you, they are available with high res non-glare screens.
The only bummer with the T520 is the position of the ExpressCard slot, which is on the right hand side, closest to the front of the laptop. As a right-hander used to moving my mouse in this region it is a little frustrating, but hardly a showstopper. Anyway, the Lenovo's may be worth a look. I chanced upon a good 2nd-hand model that was effectively brand-new, and tried it out knowing I could on-sell it quickly if it was not suitable. Luckily it has been fine so far.